DE4039950A1 - 1-Alkenyl ether prodn. form di:alkyl acetal - by heating in presence of amine and acid, intermediates for pharmaceuticals, plant protection agents, etc. - Google Patents

Abstract

Prodn. of ethers of formula R1-CR2=CH-OR3 (I) comprises reacting, at elevated temp., an acetal R1-CHR2-CH(OR3)2 (II) in presence of a catalyst consisting of an acid (III) and an amine (IV). R1 = 1-6C residue; R2 = H or 1-2C residue; R3 = 1-6C residue. - More specifically, (III) is 0.00015-0.008 (0.00025-0.0015) mole per mole (II) and the acid:amine mole ratio 1:0.7-3.5 (1:1-2). The reaction is at above the b.pt. of the reaction prods., esp. not over 200 (160) deg.C..

Description

The present invention relates to a process for the preparation of ethers of the formula R ¹ -CR ² = CH-OR ³ , wherein R ¹ for a radical with 1 to 6 carbon atoms, R ² for hydrogen or a radical with 1 to 2 carbon atoms and R ³ represents a radical having 1 to 6 carbon atoms. Owing to their properties, ethers of the type mentioned above are important for a number of technical applications. They can be used as important building blocks and raw materials for the synthesis of specialty chemicals, pharmaceuticals, natural products and crop protection agents.

DE-PS 28 44 635 describes a process for the manufacture lung of 2-propyl-pent-4-en-1-al, which consists of n-valer aldehyde and 2 moles of allyl alcohol produced in Presence of an acid catalyst, for example p-To luolsulfonic acid, split and the intermediate formed Ether is thermally rearranged.

The US-PS 30 23 250 relates to the production of halogen sub correspond to substituted, unsaturated ether by cleavage chender 1,1-di (2-haloalkoxy) alkanes in the presence strong mineral acids or aromatic sulfonic acids, the are not volatile under the reaction conditions. The reaction mixture resulting from the cleavage reaction you set a rela within a distillation column tiv low-boiling, nitrogen-containing base, at for example an amine, too. The addition of nitrogen ent holding base serves to neutralize the spal of the halogen-containing diacetal Links.  

L.A. Yanovskaya et al. describe in Otdel. Khim. Nauk 1960 1246 to 1253 (Chem Abstr. 54, 24 452 g (1960)) Process for the production of unsaturated ethers, wherein a corresponding aldehyde diacetal in the presence of one p-Toluenesulfonic acid and quinoline existing catalyst with the elimination of alcohol to the unsaturated ether is implemented. The yields obtained depend on between the unsaturated ether to be produced between 40 and 70%.

There is therefore a need for a method that on the one hand, only a small effort to implement it requires and on the other hand not only on the Production of a few, especially unsaturated Limited ether, but a variety of unsaturated Makes ether accessible. The procedure is also to ei ner reduction of unwanted by-products and to lead directly to an increase in the product yield.

This object is achieved by a process for the preparation of ethers of the formula R ¹ -CR ² = CH-OR ³ , wherein R ¹ for a radical with 1 to 6 carbon atoms, R ² for hydrogen or a radical with 1 to 2 carbon atoms and R ^{3 represents} a radical having 1 to 6 carbon atoms, characterized in that a diacetal of the formula R ¹ -CHR ² -CH (-OR ³ ) _{2 is} reacted at elevated temperature in the presence of a catalyst consisting of an acid and an amine becomes.

R ¹ represents a radical with 1 to 6, in particular 1 to 4, preferably 1 to 3 carbon atoms. Examples of R ¹ include, in particular, aliphatic straight-chain or branched radicals. R ¹ represents a methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, n-pentyl, i-pentyl, 2-methylbutyl, 3-methylbutyl , n- hexyl, i-hexyl, especially methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, preferably methyl, ethyl, n-propyl and i Propyl radical.

R² comprises hydrogen or a radical having 1 to 2 carbon atoms, in particular a methyl or ethyl radical.

R³ stands for a radical with 1 to 6, in particular 1 to 4, preferably 1 to 3 carbon atoms. As examples for R³ are in particular aliphatic straight-chain or branched radicals, such as a methyl, ethyl, n-propyl, i- Propyl, n-butyl, i-butyl, n-pentyl, i-pentyl, 2- Methylbutyl, 3-methylbutyl, n-hexyl, i-hexyl, especially Methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, preferably methyl, ethyl, n-propyl and i- To name propyl radical.

The inventive method is based on a diacetal of the formula R ¹ -CHR ² -CH (-OR ³ ) ₂ , wherein R ¹ , R ² and R ^{3 have} the meaning described above, as a starting material. Such diacetals are obtained by reacting an aldehyde with an alcohol, the aldehyde group reacting with 2 alcohol molecules to form water. This reaction is usually carried out in the presence of acidic catalysts and the water of reaction formed is removed by azeotropic distillation with the aid of a suitable solvent. A mineral acid, for example sulfuric acid or phosphoric acid, or an aliphatic or aromatic sulfonic acid can be used as the catalyst. Suitable solvents are all organic solvents that form a corresponding acetrope with water. These include aliphatic hydrocarbons, cyclohexane, cyclohexane derivatives, toluene and xylene. In many cases, cyclohexane has proven to be a particularly suitable solvent.

According to another variant, the aldehyde is set with the Alcohol in the presence of the solvent and acid Catalyst at relatively low temperatures around, new This is due to the added solvent heterogeneous reaction mixture separates the usual Water phase that arises as the lower layer and then removes the solvent from the orga African phase by distillation, if necessary reduced pressure. The remaining distillation back who already had the desired diacetal of the aldehyde contains in high concentration, can be directly in the inventive methods are used.

The diacetal is made in the presence of an acid and implemented an amine existing catalyst. The need acidity is quite low. Per mole of diacetal, 0.00015 to 0.008, especially 0.0002 to 0.006, preferred 0.00025 to 0.0015 mol acid used.

When choosing the acid, care should be taken that it has sufficient acidity. The acid should a pK value of 2.5, in particular 2.2, preferably 2.0 exhibit.

Suitable acids are phosphoric acid and some of it esterified derivatives, sulfuric acid, sulfuric acid half esters, aliphatic or aromatic sulfonic acids, ins special aromatic sulfonic acids. As well suited have benzenesulfonic acid and toluenesulfonic acid, ins special p-toluenesulfonic acid.

The amine has been found to be advantageous not to be used in any quantity, but certain Ratios of quantities to be observed. The molar ratio of  Acid to amine should be 1: 0.7 to 1: 3.5, especially 1: 0.8 to 1: 3, preferably 1: 1 to 1: 2.

The amine which acts as a catalyst component should not be volatile under the reaction conditions and consequently have a boiling point that is at least 10, in particular 20, preferably 30 ° C above the boiling point the resulting reaction products. As amines can be primary, secondary and / or tertiary amines use.

The criterion for a selection of suitable amines is Number of all carbon atoms present in the amine move. The amine should total 8 to 30, in particular 9 to 24, preferably 10 to 20 carbon atoms.

Suitable amines are cycloaliphatic and aliphatic Amines, especially straight-chain and / or branched aliphatic amines.

Examples of amines are n-octyl, n-nonyl, n-decyl, n- Dodecyl, 2-ethylhexyl, i-nonyl, 3,5,5-trimethylhexyl, Di-n-butyl, di-i-butyl, diamyl, di-n-hexyl, di-n octyl, di-2-ethylhexyl, di-i-nonyl, tri-n-propyl, Tri-n-butyl, tri-n-pentyl, tri-n-hexyl, tri-n-octyl, Tri-2-ethylhexyl, tri-n-nonyl, tri-i-nonyl and tri-n decylamine.

In many cases, isononylamine, diamylamine, Tri-n-butylamine, di-2-ethylhexylamine and diisononylamine Proven as an amine.

Amines are not understood to be nitrogen-containing products rocyclic compounds, for example from the series of pyridines, pyrimidines, pyrroles, pyrazoles and their Derivatives.  

To carry out the process according to the invention, the catalyst system consisting of the acid and the amine is added to the diacetal, the mixture is heated with mixing and the reaction products formed in the course of the reaction, namely the alcohol split off and the unsaturated ether of the formula R ¹ -CR, are separated ² = CH-OR ³ , from. The process according to the invention can be carried out discontinuously - for example using an agitator tank - or continuously - for example by means of a cascade of stirred tanks, a bubble cap column, packed column. The reaction takes place in the liquid phase, a temperature being maintained which is above the boiling point of the reaction products.

Open-chain diacetals, which preferably have two identical acetal residues, are suitable as the diacetal of the formula R ¹ -CHR ² -CH (-OR ³ ) ₂ . Examples of such diacetals are dimethylacetals, diethylacetals, di-n-propylacetals, di-n-butylacetals, di-i-butylacetals, di-n-pentylacetals, di-i-pentylacetals, di-n-hexylacetals and di-i-hexylacetals of aldehydes of the general formula R ¹ -CHR ² -CHO, in which R ^{1 represents} a radical having 1 to 6 carbon atoms and R ^{2 represents} hydrogen or a radical having 1 to 2 carbon atoms.

Examples of such diacetals are

Acetylaldehyde dimethyl acetal, Acetaldehyde diethylacetal, acetaldehyde dipropylacetal, Propionaldehyde dimethylacetal, propionaldehyde diethylacetal, Propionaldehyde dipropylacetal, propionaldehyde dibutylacetal, butyraldehyde dimethylacetal, butyraldehyde diethylacetal, butyraldehyde-dipropylacetal, Butyraldehyde dibutylacetal, butyraldehyde dipentylacetal, Valeraldehyde-dimethylacetal, valeraldehyde-diethylacetal,  Valeraldehyde dipropylacetal, valeraldehyde dibutylacetal, Valeraldehyde-dipentylacetal, isovaleraldehyde-dimethylacetal, Isovaleraldehyde diethylacetal, isovaleraldehyde dipropylacetal, isovaleraldehyde-dibutylacetal, isovaleraldehyde- dipentylacetal, hexanal-dimethylacetal, hexanal- diethylacetal, hexanal-dipropylacetal, hexanal-dibutylacetal, Hexanal-dipentylacetal, hexanal-dihexylacetal, 2-ethylhexanal-dimethylacetal, 2-ethylhexanal-diethylacetal, 2-ethylhexanal dipropylacetal, 2-ethylhexanal dibutylacetal, 2-ethylhexanal-dipentylacetal, 2-ethylhexanal- dipentylacetal and 2-ethylhexanal dihexylacetal.

Propanal di have been found to be particularly suitable methyl acetal, propanal diethyl acetal, propanal diisopro pylacetal, propanal-di-n-propylacetal, butanal-dimethyl acetal, butanal-diethylacetal, butanal-diisopropylacetal, Butanal-di-n-propylacetal and valeraldehyde diethylacetal proven.

The reaction is usually carried out at normal pressure or performed slightly increased pressure, but it is also possible to run it under reduced pressure. Anyone can do without the addition of a solvent the.

The reaction temperature is too dependent on the pressure should usually choose a maximum of 220 to 240 ° C be. In most cases the implementation can at temperatures of at most 200, in particular 180, preferably carry out 160 ° C with good success. That from the Acid and the amine existing catalyst system remains after separation of the reaction products formed as Residue and can optionally again as a catalyst be used in the inventive method.  

The following examples demonstrate the invention without limit them.

Experimental part I. Production of the starting materials (A) Preparation of Proportionaldehyde Diethyl Acetal

In one with stirrer, dropping funnel, reflux condenser and 4-liter three-neck flasks equipped with an internal thermometer 553.2 g of ethanol, 900 g of cyclohexane and 5.7 g of p-toluene submitted sulfonic acid and within 5 minutes Stir mixed with 348.6 g of propionaldehyde. As a result of spontaneous onset of acetal formation increases the internal temperature temperature up to about 40 ° C. The mixture is left at 40 ° C. for 30 minutes react, then provides by adding sodium bicarbonate alkali (20% aqueous solution) in the reaction mixture, the from a lower water phase and an upper organi phase exists, a pH of 7.0 and separates the water phase.

The orga is distilled to remove the low boilers African phase at 1013 mbar up to a bottom temperature from 121 ° C.

After removal of the low boilers, 532.2 g of product of the following composition remain (determined by gas chromatographic analysis):
0.6% by weight of ethanol,
0.1% by weight propionaldehyde,
3.8% by weight of cyclohexane,
93.8% by weight of propionaldehyde diethylacetal,
1.7% by weight of other components.

B): Preparation of n-butyraldehyde-di-n-butyl acetal

In one with stirrer, dropping funnel, reflux condenser and 4-liter three-neck flasks equipped with an internal thermometer 889.5 g of n-butanol, 1500 g of cyclohexane and 5.7 g of p-toluene submitted olsulfonic acid and within 5 minutes 432.7 g of n-butyraldehyde were added with stirring. As a result of spontaneous onset of acetal formation increases the internal temperature temperature up to about 35 ° C. Leave at 35 for 30 minutes react to 40 ° C, then provides by adding Sodium hydroxide solution (20% aqueous solution) in the reaction mixture, that of a lower water phase and an upper orga phase, there is a pH of 7.0 and separates the water phase.

The orga is distilled to remove the low boilers African phase at 200 mbar up to a bottom temperature from 160 ° C.

After removal of the low boilers, 973.0 g of product of the following composition remain (determined by gas chromatographic analysis):
2.3% by weight of n-butanol,
0.1% by weight of n-butyraldehyde,
0.1% by weight of cyclohexane,
95.7% by weight of n-butyraldehyde di-n-butyl acetal,
1.8% by weight of other components.

C): Preparation of 3-methylbutyraldehyde di-n-propylacetal

In one with stirrer, dropping funnel, reflux condenser and 4-liter three-neck flasks equipped with an internal thermometer 841.4 g of n-propanol, 1750 g of cyclohexane and 6.7 g of p-toluene  submitted olsulfonic acid and within 5 minutes 602.7 g of 3-methylbutyraldehyde were added with stirring. As a result the spontaneous onset of acetal formation increases the inside temperature up to about 35 ° C. Allow 30 minutes 35 to 40 ° C react, then sets by adding of sodium hydroxide solution (20% aqueous solution) in the reaction mix that of a lower water phase and an upper organic phase, a pH of 7.0 and separates the water phase.

The orga is distilled to remove the low boilers African phase at 200 mbar up to a bottom temperature from 100 ° C.

After removal of the low boilers, 941.5 g of product of the following composition remain (determined by gas chromatographic analysis):
4.5% by weight n-propanol,
0.3% by weight of 3-methylbutyraldehyde,
0.2% by weight of cyclohexane,
91.9% by weight of 3-methylbutyraldehyde di-n-propylacetal,
3.1% by weight of other components.

D): Preparation of 2-ethylbutyraldehyde dimethyl acetal

In one with stirrer, dropping funnel, reflux condenser and 4-liter three-neck flasks equipped with an internal thermometer 417.3 g of methanol, 1625 g of cyclohexane and 6.2 g of p-toluene submitted sulfonic acid and within 5 minutes Stirred with 651.3 g of 2-ethylbutyraldehyde. As a result the spontaneous onset of acetal formation increases the inside temperature up to about 32 ° C. Allow 30 minutes 40 ° C react, then by adding Sodium hydroxide solution (20% aqueous solution) in the reaction mixture,  that of a lower water phase and an upper orga phase, there is a pH of 7.0 and separates the water phase.

The orga is distilled to remove the low boilers African phase at 200 mbar up to a bottom temperature from 105 ° C.

After removal of the low boilers, 760.7 g of product of the following composition remain (determined by gas chromatographic analysis):
0.1% by weight of cyclohexane,
0.3% by weight of 2-ethylbutyraldehyde,
97.9% by weight of 2-ethylbutyraldehyde dimethyl acetal,
1.7% by weight of other components.

II. Preparation of the α, β-unsaturated ethers IIa) Preparation of ethyl 1-propenyl ether example 1

In one with a column (24 theoretical plates) 2-liter round bottom flasks are 800 g propionaldehyde di ethyl acetal (prepared as described under (A)), 0.57 g p-toluenesulfonic acid and 1.13 g di-2-ethylhexylamine submitted and heated. It is distilled as a result of Reaction products released by acetal splitting (ethanol and ethyl 1-propenyl ether) under a reflux ratio from 3: 1 and a pressure of 1013 mbar. The tempera tur at the top of the column is 67 to 70 ° C. The Destil lation is terminated as soon as a bottom temperature of 220 ° C is reached. 775.4 g of distillate are obtained. The Yield of ethyl 1-propenyl ether is 98.2% of the Theory, based on the acetal used.  

Comparative Example 1

The procedure is as given in Example 1, but without Addition of di-2-ethylhexylamine. 748.5 g are obtained Distillate.

The yield of ethyl 1-propenyl ether is 34.0% of the Theory, based on the acetal used.

Example 2

The procedure is as given in Example 1, but under Add 0.28 g p-toluenesulfonic acid and 0.57 g di-2- ethylhexylamine, and receives 760.5 g of distillate.

The yield of ethyl 1-propenyl ether is 95.9% of the Theory, based on the acetal used.

Example 3

The procedure is as given in Example 1, but under Add 0.28 g p-toluenesulfonic acid and 1.13 g di-2- ethylhexylamine, and receives 754.5 g of distillate.

The yield of ethyl 1-propenyl ether is 85.5% of Theory, based on the acetal used.

Example 4

The procedure is as given in Example 1, but under Add 1.44 g p-toluenesulfonic acid and 2.84 g di-2- ethylhexylamine, and receives 758.5 g of distillate.  

The yield of ethyl 1-propenyl ether is 93.2% of the Theory, based on the acetal used.

Example 5

The procedure is as given in Example 1, but under Add 5.68 g p-toluenesulfonic acid and 11.36 g di-2- ethylhexylamine, and receives 735.5 g of distillate.

The yield of ethyl 1-propenyl ether is 89.1% of the Theory, based on the acetal used.

Example 6

The procedure is as given in Example 1, but under Add 0.57 g p-toluenesulfonic acid and 0.72 g di-2- ethylhexylamine, and receives 772.7 g of distillate.

The yield of ethyl 1-propenyl ether is 97.8% of the Theory, based on the acetal used.

Example 7

The procedure is as given in Example 1, but under Add 0.57 g p-toluenesulfonic acid and 0.58 g di-2- ethylamine, and receives 755.4 g of distillate.

The yield of ethyl 1-propenyl ether is 91.7% of the Theory, based on the acetal used.

Example 8

The procedure is as given in Example 1, but under Add 0.57 g p-toluenesulfonic acid and 1.44 g di-2- ethylhexylamine, and receives 769.9 g of distillate.  

The yield of ethyl 1-propenyl ether is 97.6% of the Theory, based on the acetal used.

Example 9

The procedure is as given in Example 1, but under Add 0.57 g p-toluenesulfonic acid and 0.68 g isono nylamine (made by hydroformylation of Diisobu tylen and subsequent reductive amination), and he holds 773.8 g distillate.

The yield of ethyl 1-propenyl ether is 98.1% of the Theory, based on the acetal used.

Example 10

The procedure is as given in Example 1, but under Add 0.57 g p-toluenesulfonic acid and 1.28 g diisono nylamine (made by hydroformylation of Diisobu tylen and subsequent reductive amination), and he holds 708.3 g of distillate.

The yield of ethyl 1-propenyl ether is 97.1% of the Theory, based on the acetal used.

Example 11

The procedure is as given in Example 1, but under Add 0.57 g p-toluenesulfonic acid and 0.75 g diamyl amine, and receives 771.5 g of distillate.

The yield of ethyl 1-propenyl ether is 97.8% of the Theory, based on the acetal used.  

Example 12

The procedure is as given in Example 1, but under Add 0.28 g p-toluenesulfonic acid and 0.44 g tri-n- butylamine, and receives 765.3 g of distillate.

The yield of ethyl 1-propenyl ether is 96.9% of the Theory, based on the acetal used.

The composition of the distillate obtained in each of the preceding examples (determined by gas chromatography) is shown in Table 1 below.

IIb) Preparation of butyl 1-butenyl ether Example 13

800 g of n-butyraldehyde-di-n-butyl acetal (prepared as described under (B)), 0.19 g of p-toluenesulfonic acid and 0.38 are in a 2-liter round-bottom flask fitted with a column (24 theoretical plates) g of di-2-ethylhexylamine and heated. The reaction products released as a result of the acetal cleavage (n-butanol and butyl-1-butenyl ether) are distilled off under a reflux ratio of 0.5: 1 and a pressure of 200 mbar. The temperature at the top of the column is 74 to 81 ° C. The distillation is ended as soon as a bottom temperature of 200 ° C. is reached. 770.2 g of distillate follow the composition (determined by gas chromatography):
37.4% by weight of n-butanol,
0.1% by weight of n-butyraldehyde,
0.1% by weight of cyclohexane,
60.3% by weight of butyl 1-butenyl ether,
1.1% by weight of n-butyraldehyde di-n-butyl acetal,
1.0% by weight of other components.

The yield of butyl 1-butenyl ether is 95.8% of the Theory, based on the acetal used.

Comparative Example 2

The procedure is as in Example 13, but without the addition of di-2-ethylhexylamine, and 763.1 g of distillate of the following composition (determined by gas chromatography) are obtained:
23.1% by weight of n-butanol,
0.1% by weight of cyclohexane,
35.5% by weight of butyl 1-butenyl ether,
39.8% by weight of n-butyraldehyde di-n-butyl acetal,
1.5% by weight of other components.

The yield of butyl 1-butenyl ether is 55.8% of the Theory, based on the acetal used.

Example 14

The procedure is as in Example 13, but with the addition of 0.38 g of p-toluenesulfonic acid and 0.76 g of di-2-ethylhexylamine, and 778.2 g of distillate of the following composition (determined by gas chromatography):
37.8% by weight of n-butanol,
0.1% by weight of n-butyraldehyde,
0.1% by weight of cyclohexane,
61.3% by weight of butyl 1-butenyl ether,
0.2% by weight of n-butyraldehyde di-n-butyl acetal,
0.5% by weight of other components.

The yield of butyl 1-butenyl ether is 98.3% of the Theory, based on the acetal used.

IIc) Preparation of 3-methyl-1-butenylpropyl ether Example 15

800 g of 3-methylbutyralde hyd-di-n-propylacetal (prepared as described under (C) be), 0.2 g of p-toluenesulfonic acid and 0 are in a 2-liter round bottom flask equipped with one column (24 theoretical plates) , 39 g of di-2-ethylhexylamine and heated. The reaction products released as a result of the acetal cleavage (n-propanol and 3-methyl-1-butenylpropyl ether) are distilled off under a reflux ratio of 1: 1 and a pressure of 200 mbar. The temperature at the top of the column is 60 to 63 ° C. The distillation is ended as soon as a bottom temperature of 200 ° C is reached. 775.6 g of distillate of the following composition (determined by gas chromatography):
34.7% by weight of n-propanol,
0.2% by weight of 3-methylbutyraldehyde,
0.2% by weight of cyclohexane,
63.9% by weight of 3-methyl-1-butenylpropyl ether,
0.2% by weight of 3-methylbutyraldehyde di-n-propylacetal,
0.8% by weight of other components.

The yield of 3-methyl-1-butenylpropyl ether is 99.0% of theory, based on the acetal used.

Comparative Example 3

The procedure is as in Example 15, but without the addition of di-2-ethylhexylamine, and 765.5 g of distillate of the following composition (determined by gas chromatography):
32.0% by weight of n-propanol,
0.3% by weight of 3-methylbutyraldehyde,
0.2% by weight of cyclohexane,
58.2% by weight of 3-methyl-1-butenyl propyl ether,
6.5% by weight of 3-methylbutyraldehyde di-n-propylacetal,
2.8% by weight of other components.

The yield of 3-methyl-1-butenylpropyl ether is 89.0% of theory, based on the acetal used.  

II) Preparation of 2-ethyl-1-butenyl methyl ether Example 16

In one with a column (24 theoretical plates) 2-liter round bottom flasks are 720 g of 2-ethylbutyraldehyde dimethyl acetal (prepared as described under (D)), 0.48 g p-toluenesulfonic acid and 0.96 g 2-ethylhexylamine submitted and heated. It is distilled as a result of Reaction products released by acetal cleavage (methanol and 2-ethyl-1-butenyl methyl ether) under reflux ratio of 10: 1 and a pressure of 1013 mbar. The temperature at the top of the column is 104 to 115 ° C. The distillation is stopped as soon as a bottom temperature of 200 ° C is reached.

This gives 692.5 g of distillate of the following composition (determined by gas chromatography):
21.4% by weight of methanol,
0.1% by weight of cyclohexane,
0.4% by weight of ethyl butyraldehyde,
77.1% by weight of 2-ethyl-1-butenyl methyl ether,
0.1% by weight of 2-ethylbutyraldehyde dimethyl acetal,
0.9% by weight of other components.

The yield of 2-ethyl-1-butenyl methyl ether is 97.0% of theory, based on the acetal used.

Comparative Example 4

The procedure is as in Example 16, but with 0.48 g of p-toluenesulfonic acid, but without the addition of 2-ethyl hexylamine, and 683.2 g of distillate having the following composition (determined by gas chromatography):
19.6% by weight of methanol,
0.1% by weight of cyclohexane,
0.4% by weight of 2-ethylbutyraldehyde,
70.1% by weight of 2-ethyl-1-butenyl methyl ether,
8.1% by weight of 2-ethylbutyraldehyde dimethyl acetal,
1.7% by weight of other components.

The yield of 2-ethyl-1-butenyl methyl ether is 87.0% of theory, based on the acetal used.

Claims (10)

1. A process for the preparation of ethers of the formula R ¹ -CR ² = CH ² -OR ³ , wherein R ¹ for a radical with 1 to 6 carbon atoms, R ² for hydrogen or a radical with 1 to 2 carbon atoms and R ³ for one The radical having 1 to 6 carbon atoms is characterized in that a diacetal of the formula R ¹ -CHR ² -CH (-OR ³ ) _{2 is} reacted in the presence of a catalyst consisting of an acid and an amine at elevated temperature. 2. The method according to claim 1, characterized in that 0.00015 to 0.008 per mole of diacetal, in particular 0.0002 to 0.006, preferably 0.00025 to 0.0015 mol Acid can be used. 3. The method according to claim 1 or 2, characterized records that acid to amine in a molar ratio of 1: 0.7 to 1: 3.5, in particular 1: 0.8 to 1: 3, preferably 1: 1 to 1: 2. 4. The method according to one or more of claims 1 to 3, characterized in that the acid a pK value 2.5, in particular 2.2, preferably 2.0 having. 5. The method according to one or more of claims 1 to 4, characterized in that as the acid Phos phosphoric acid, sulfuric acid, an aliphatic or aromatic sulfonic acid, especially an aromatic cal sulfonic acid is used.   6. The method according to one or more of claims 1 to 5, characterized in that as the acid p-toluene olsulfonic acid is used. 7. The method according to one or more of claims 1 to 6, characterized in that an amine as amine with a total of 8 to 30, especially 9 to 24, before adds 10 to 20 carbon atoms. 8. The method according to one or more of claims 1 to 7, characterized in that an ali phatic straight-chain and / or branched amine, in particular n-hexyl, n-heptyl, n-octyl, n-decyl, n-dodecyl, 2-ethylhexyl, i-nonyl, 3,5,5-trimethylhexyl, Di-n-butyl, di-i-butyl, diamyl, di-n hexyl, di-n-octyl, di-2-ethylhexyl, di-i-nonyl, Tri-n-propyl, tri-n-butyl, tri-n-pentyl, tri-n hexyl, tri-n-octyl, tri-2-ethylhexyl, tri-n-nonyl, Tri-i-nonyl and tri-n-decylamine used. 9. The method according to one or more of claims 1 to 8, characterized in that the implementation at a temperature above the boiling point of the formed reaction products is carried out. 10. The method according to one or more of claims 1 to 9, characterized in that the temperature at most 200, in particular 180, preferably 160 ° C. is.